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Old 29-05-2009, 12:05   #1
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Idling Too Long?

I heard somewhere that it was bad to run a diesel engine not under load for extended periods of time? I have been doing a lot of dockside testing and was wondering if I was damaging the engine?
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Old 29-05-2009, 12:21   #2
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Only if you let it idle for long periods of time. Letting it idle while doing checks and stuff like that won't hurt it. You have to let it idle for hours before you will worry about the fuel washing the oil off the cylinder liners. Biggest thing is that the engine starts running cold, fuel doesn't ignite properly, and thats what causes the excess unburnt fuel to wash the lubrication off the cylinder walls...Plus other issues like low oil pressure and the bearings not getting proper lubrication..
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Old 29-05-2009, 13:09   #3
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not a bad idea to tie those lines off good and give it good workout occassionally at the dock now and then too..
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Old 29-05-2009, 13:13   #4
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not a bad idea to tie those lines off good and give it good workout occassionally at the dock now and then too..
I try not to do this because is usually means we are spending too much time on the dock.

We occasionally let the engine idle around 1100 rpm for an hour while the batteries charge and the beers cool down. Do you think this is long enough damage the engine?
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Old 29-05-2009, 13:17   #5
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Nope, that's pretty much the ritual cruising right? 1- 1.5 hours per day at high idle to charge them up . However, if you have a pretty high output alternator, you are running some decent load on it for 20 mins or so anyway....
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Old 29-05-2009, 14:08   #6
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On our last boat we had an old saltwater cooled volvo engine with an undetermined number of hours when we bought it. Over the next 5 years we ran the engine either daily or every other day to charge the batteries, unless we happened to be going somewhere and it got a little bit of load. It finally, after 5 years of this abuse, started running hot and we had to clean the carboned up exhaust manifold. Then we subjected it to another year of constant idling before selling the boat with the engine running fine. In other words, it's not good to idle the engine, just like drinking a beer is not good for you.
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Old 29-05-2009, 14:20   #7
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Unbusted,
Diesel engine experts in my company (I work in naval shipbuilding) warned me that running a Diesel engine at medium or high rpm without load (resisting torque) for some time results in glazing the inside of the cylinders and finally wearing down the engine prematurely. At low rpm, you might have soot building up in the engine from low-temperature combustion.

When I have to run the engine while docked or moored, I just engage the astern gear to provide some resisting torque: for the same absorbed torque, the propeller provides less thrust when making astern turns than when making ahead turns. This is softer on the mooring lines.

Of course, increasing the absorbed power increases the fuel consumption but it's a small sacrifice.

Alain
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Old 29-05-2009, 14:32   #8
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Don't worry about idling the engine. If you have a fresh water cooled engine with a working thermostat it will not be "cold". As far as "washing the lubrication off the cylinders", if you don't have worn out injectors that dribble too much fuel that won't happen either. Remember, the purpose of oil control rings on the pistons is to scrape the excess oil off of the cylinder walls. Yes, oil pressure is lower at low engine speeds, but there is also little load to wear on the bearings.

Bottom line is this, 10,000 over the road truck drivers idle their rigs for hours every day while they sleep. Doesn't seem to hurt those big rigs that they earn their living with.
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Old 29-05-2009, 14:45   #9
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I've never understood the problem with low rpm. I have been looking at a power boat with 2 500hp Yanmars. The builder gives fuel range at 1500 rpm - Trucks sit in truck stops with their engines idleing for hours. What makes sailboat diesels different?
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Old 29-05-2009, 16:45   #10
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I suggest you take Hydra's advice as no load will allow the bores to glaze up. Without load the ring pressure on the bores is not high enough. Correct running temperature (hot) Oil changed regulary with mono grade not Multi. Engine run always under load (alternator is not enough load). An engine run this way will give you a very long life span. Its the load not RPM some of the very large container ship engines only turn 100RPM.
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Old 29-05-2009, 16:47   #11
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But those trucks go out on the road once the driver is awake and the pedal is frequently flat to the floor. Spent a few years driving them and that's how you get up hills, foot to the floor and work the shifter. That hard work offsets the crud that idling builds up.
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Old 29-05-2009, 19:34   #12
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Some engines can tolerate long idling or fast idle periods to charge batteries or cool refrigerators better than others. I would trust a Yanmar or Kubota based engine but never a Mitsubishi based engine...
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Old 30-05-2009, 01:55   #13
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Bottom line is this, 10,000 over the road truck drivers idle their rigs for hours every day while they sleep. Doesn't seem to hurt those big rigs that they earn their living with.
Just hurts the environment. I always found that sort of lame. My diesel consumption, however, in somehow holier.
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Old 30-05-2009, 04:30   #14
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I've never understood the problem with low rpm... Trucks sit in truck stops with their engines idleing for hours. What makes sailboat diesels different?
I agree. Neither you, nor those truck operators understand idling issues.

Excessive idling produces sulphuric acid that breaks down the oil and eats into bearings, rings, valve stems and engine surfaces, which can increase maintenance costs and shorten the life of the engine. Idling wadtes fuel, and releases unnecessary emissions.

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... Bottom line is this, 10,000 over the road truck drivers idle their rigs for hours every day while they sleep. Doesn't seem to hurt those big rigs that they earn their living with.
That’s not what the engine manufacturers and other experts say.

Detroit Diesel ➥ Diesel engine idling, from an authority: Detroit Diesel BusBuilding.com

Cummins ➥ http://www.planningforpeople.ca/is/s...ee_Cummins.pdf

NRCAN ➥ Technical Evaluation of Automatic-Type Transmissions for the Heavy Truck Market

USEPA ➥ http://www.epa.gov/NE/eco/diesel/ass...uck_Idling.pdf

FWIW: You'll never see an idling UPS truck or tractor without a driver in it.
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Old 30-05-2009, 04:41   #15
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Some engines can tolerate long idling or fast idle periods to charge batteries or cool refrigerators better than others. I would trust a Yanmar or Kubota based engine but never a Mitsubishi based engine...
Really?

I have owned all three and so far the Mitsubishi has been the absolute most reliable. I say this as she sits with over 2900 hours on her!

This is the top end at 2878 hours.


Oh and a LOT of these hours are IDLING running my Sea Frost refrigeration.

She has only ever had Shell Rotella 15W-40..
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